High speed document encoders are widely utilized for encoding continuously moving documents. For example, the processing of checks, deposit slips, remittance stubs and similar financial documents normally includes encoder apparatus for magnetically encoding MICR (Magnetic Ink Character Recognition) indicia on these documents. Representing an important component of such encoder apparatus is an operably controlled printer employing an ink ribbon advanced past the print head. The ink ribbon, typically of a pressure transfer type in which, for example, the magnetic ink is transferred to the document, is advanced from a supply reel having a prewound quantity of fresh ribbon thereon through the print head station, and at a rate, synchronized with operation of the printer, and thereafter is wound onto a takeup reel.
Being that the ink on the ribbon is consumable, periodic replacement is required in order to maintain a fresh ribbon supply for operation of the printer. In view of the required speed of the overall document, processing, it is therefore desirable that this ribbon replacement be accomplished as rapidly as possible to avoid undesirable delays in processing; therefore the ribbon supply apparatus should effectively meet such objective. In addition, the rapid movement of the ribbon between supply and takeup requires some type of buffering means for the ribbon, not only to enable such rapid movement, but to absorb ribbon shock during startup and high speed reversals.